In the manufacture of motor vehicles, glass components, such as windshields, side windows and backlights, are joined to the metal vehicle body by means of an elastomeric adhesive material which may also function as a sealant. The adhesive materials which are used for this purpose are required to meet a number of criteria including appearance, ease of application, shear strength, and adhesion in crash tests. Therefore, good adhesion is required between the adhesives and the various nonporous metal, glass and polymeric substrates to which it is bonded.
In order to obtain acceptable levels of adhesion between the adhesives and the nonporous surfaces, various primers have been used to precoat the nonporous surfaces to enable the adhesive to bond better to them. In original equipment manufacture and glass replacement processes, primers are generally applied to both the metal and glass surfaces prior to application of the adhesive. The metal surfaces may be aluminum or steel, and may be bare, treated, or coated with various types of paints or enamels. Various polymeric materials may also be used in place of the glass components, or as structural members in place of the metal components. A current technique for joining glass to metal in vehicles uses an elastomeric urethane or silylated urethane adhesive. Other elastomeric adhesives which can be used include silyl-terminated polyethers and silicones. All of these adhesives may also be used to bond polymeric substrates to glass or metal, or to each other.
A number of primer compositions have been proposed for promoting adhesion between urethane adhesives or sealants and nonporous materials in technologies relating to motor vehicle manufacture as well as other areas.
For example, U.S. Pat. No. 3,707,521, and its divisional, U.S. Pat. No. 3,779,794, discuss a polyurethane adhesive primer composition comprising a branched polyurethane polymer in combination with a latent catalyst for the moisture curing of free isocyanate groups present.
U.S. Pat. No. 4,882,003 is directed to sealant primer compositions useful for promoting adhesion to enamel paint coated substrates, in which the primer comprises an acrylic polymer base composition, pigment, and a solvent effective to interpenetrate the enamel substrate coating.
U.S. Pat. No. 4,857,366 describes the use of a primer solution of p-toluenesulfonic acid and an organofunctional silane in solvent prior to applying an uncured urethane sealant to painted or glass surfaces.
U.S. Pat. No. 4,625,012, incorporated herein by reference for its discussion of isocyanatosilane adducts, describes a method of making a polyurethane polymer by reacting an isocyanatosilane adduct having at least two isocyanato groups with another isocyanate and a polyol.
U.S. Pat. No. 5,238,993 is directed to a primer comprising a solution of a polyester resin derived from a carboxylic acid and a glycol, an isocyanate and a silane-containing moiety dissolved in a particular mixture of solvents.
Because of the different properties of the various coated and uncoated metal, glass and polymeric substrates, different primers have been used on different types of substrates to obtain optimal adhesion with the adhesives. That is, each nonporous surface being bonded may require its own specific type of primer. Furthermore, primers used with urethane adhesives may not be acceptable for use with silylated urethane, silyl-terminated polyether or silicone adhesives. Therefore, a wide variety of primers have been needed to promote the bonding of different adhesives to different glass, metal and polymeric substrates.
For original equipment manufacturers, it may be reasonable to select a specific primer for a particular combination of adhesive and substrate, and to use different primers on the metal, glass and polymeric surfaces. However, for glass replacement operations working with a variety of metal, glass and polymeric substrates, as well as various adhesive materials, it can be very difficult to maintain and use a wide variety of different primers.
Thus, there is a need for a universal primer which can be used to promote adhesion between the various elastomeric adhesives and the different nonporous substrates to which they must adhere. There is a particular need for such a primer which can be used with the newer silylated urethanes and silyl-terminated polyethers as well as with the conventional urethane adhesives.